Kidneys of the human body function to remove excess fluids as well as some ions. The functional unit of the kidney is the nephron. A nephron consists of a filtering unit of tiny blood vessels called a glomerulus attached to a tubule. When blood enters the glomerulus, it is filtered and the remaining fluid then passes along the tubule. In the tubule, chemicals and water are either added to or removed from this filtered fluid according to the body's needs, and the final product is urine, which is excreted.
In patients with chronic kidney disease, kidney function is severely compromised. Chronic kidney disease (CKD), also known as chronic renal disease, is a progressive loss in renal function over a period of months or years. The most severe stage of CKD is End Stage Renal Disease (ESRD), which occurs when the kidneys cease to function. The two main causes of CKD are diabetes and high blood pressure, which are responsible for up to two-thirds of the cases. Heart disease is the leading cause of death for all people having CKD. Excessive fluid can accumulate in patients suffering from ESRD. The mortality rate of ESRD patients who receive traditional hemodialysis therapy is 24% per year with an even higher mortality rate among diabetic patients. Fluid accumulates in ESRD patients because the kidneys can no longer effectively remove water and other fluids from the body. The fluid accumulates first in the blood and then accumulates throughout the body, resulting in swelling of the extremities and other tissues as edema. This accumulation of fluid causes increased stress on the heart, in turn causing significant increases in blood pressure or hypertension, which can lead to heart failure.
Although the population of patients afflicted with CKD grows each year, there is no cure. Current treatments for CKD seek to slow the progression of the disease. However, as the disease progresses, renal function decreases, and, eventually, renal replacement therapy is employed to compensate for lost kidney function. Renal replacement therapy entails either transplantation of a new kidney or dialysis.
Methods to treat kidney disease require the processing of blood to extract waste components such as urea and ions. The traditional treatment for kidney disease involves dialysis. Dialysis emulates kidney function by removing waste components and excess fluid from a patient's blood. This is accomplished by allowing the body fluids, usually the blood, to come into the close proximity with the dialysate, which is a fluid that serves to cleanse the blood and actively remove the waste components and excess water. During this process, the blood and dialysate are separated by a dialysis membrane, which is permeable to water, small molecules (such as urea), and ions but not permeable to the cells. Each dialysis session lasts a few hours and may be repeated as often as three times a week.
Traditional processes, such as dialysis, require extracorporeal processing of body fluids. Once the blood is purified, it is then returned to the patient. Although effective at removing waste components from blood, dialysis treatments are administered intermittently and, therefore, do not emulate the continuous function of a natural kidney. Once the dialysis session is completed, the fluid begins to accumulate again in the tissues of the patient. The benefits of dialysis notwithstanding, statistics indicate that three out of five dialysis patients die within five years of commencing treatment. Studies have shown that increasing the frequency and duration of dialysis sessions can improve the survivability of dialysis patients. Increasing the frequency and duration of dialysis sessions more closely resembles the continuous kidney function sought to be emulated. However, the extracorporeal processing of the body fluids increases the discomfort, inconvenience and the costs associated with treatment. There is also an additional risk of infection, which mandates that the procedures be carried out under the supervision of trained medical personnel.
Wearable dialysis units have been conceived in which the various components of the dialysis unit are miniaturized and made portable. The utility of these units remains limited due to the requirement that the blood must be brought outside of the body for filtering and due to the necessity for frequent servicing of the parts.
An alternative to a wearable dialysis system is an implantable dialysis device. With conventional implantable dialysis devices, most of the components are implanted, and the blood does not leave the patient's body. This type of unit suffers from difficulties related to the need for surgery to replace the internal parts, generally resulting from growth of tissue over the surfaces of the device that are exposed to tissue fluids, which results in reduced efficiency of the filtration.
Another clinical solution for kidney disease is peritoneal dialysis. In peritoneal dialysis, dialysate is infused into the peritoneal cavity. The peritoneal membrane serves as a natural dialyzer, and waste components diffuse from the patient's bloodstream across the peritoneal membrane into the dialysis solution via an osmotic gradient. Under local anesthesia, a many-eyed catheter is sutured in place in the peritoneum and a sterile dressing is applied. The amount and the kind of dialysate and the length of time for each exchange cycle vary with the age, size, and condition of the patient. There are three phases in each cycle. During inflow, the dialysate is introduced into the peritoneal cavity. During equilibration (swell), the dialysate remains in the peritoneal cavity. By means of osmosis, diffusion, and filtration, the needed electrolytes pass via the vascular peritoneum to the blood vessels of the abdominal cavity, and the waste products pass from the blood vessels through the vascular peritoneum into the dialysate. During the third phase (drain), the dialysate is allowed to drain from the peritoneal cavity by gravity. The dialysis solution is removed, discarded, and replaced with fresh dialysis solution on a semi-continuous or continuous basis. Patients are able to replace the fluid periodically and care for the access ports. This particular treatment causes discomfort due to excess amounts of fluid being pumped in and out of the abdominal area and retrograde flow into the bloodstream, which can increase fluid retention and the risk of infections. Further, medication for pain may be necessary.
Peritoneal dialysis may result in several complications, including perforation of the bowel, peritonitis, atelectasis, pneumonia, pulmonary edema, hyperglycemia, hypovolemia, hypervolemia, and adhesions. Peritonitis, the most common problem, is usually caused by failure to use aseptic technique and is characterized by fever, cloudy dialysate, leukocytosis, and abdominal discomfort. There is a need for a dialysis system for peritoneal dialysis and/or fluid removal that is safe and effective and that markedly improves a patient's comfort and quality of life over conventional systems and methods. It would be advantageous for the system to be safe enough for continuous use and allow the patient to carry out normal daily activities. Hence, there is an unmet medical need to build a wearable or implantable medical device to treat chronic kidney disease that can provide more frequent or continuous treatment with less discomfort and a lower risk of infection.